Release the rear plate, which is thicker so that it can act as a heatsink, by removing the two long screws (with washers), and the remaining 7 screws. After the line out mod has been performed, the rear plate will not be completely removable without some unsoldering, but the unit can still be disassembled.
There is heatsink compound connecting the power amp IC to the rear plate. During reassembly, clean this area, and apply some new compound.
Remove the 2 screws which hold the upper case onto the lower case, release the ears, and lift the upper case off. There is an electrical connector between the upper and lower circuit boards which will disconnect.